Ring latch for releasably restraining a piston within a cylinder

ABSTRACT

A ring latch for releasably restraining a piston in a preselected position within a cylinder employs about the piston periphery a split ring that is maintained in an expanded latching condition by a key which fits between the ends of the split ring. Latch release is effected by withdrawing the key from its position between the ends of the split ring. Between said ends and the key, rollers are provided that are capable of rolling with respect to said ends in response to withdrawal of the key and of resetting each time the key is withdrawn.

United States Patent 1191 Skreiner 1 1 Oct. 21, 1975 [75] Inventor: Klaus M. Skreiner, Media, Pa.

[73] Assignee: General Electric Company,

Philadelphia, Pa.

22 Filed: Jan. 21, 1974 211 App]. No.: 435,142

[52] US. Cl. 92/23; 92/130; 92/193 [51] Int. Cl. FlSb 15/26 [58] Field of Search 92/23, 130, 193

[56] References Cited UNITED STATES PATENTS 1,887,384 11/1932 Welikes 92/193 2,044,499 6/1936 DAg0stino.... 92/193 X 2,261,925 11/1941 Salzer 92/30 X 2,283,961 5/1942 Williamson 92/30 X 2,986,389 5/1961 Coonrod 267/56 3,646,292 2/1972 Barkan et a1 200/82 B 3,736,844 6/1973 .lahnke 92/24 3,768,820 10/1973 Yew 1. 137/6275 X 3,812,766 5/1974 Weiss 92/25 X FOREIGN PATENTS OR APPLICATIONS 51,313 12/1919 Sweden 92/23 Primary ExaminerMartin P. Schwadron Assistant ExaminerAbraham Hershkovitz Attorney, Agent, or Firm.l. Wesley Haubner; William Freedman [57] ABSTRACT A ring latch for releasably restraining a piston in a preselected position within a cylinder employs about the piston periphery a split ring that is maintained in an expanded latching condition by a key which fits between the ends of the split ring. Latch release is effected by withdrawing the key from its position between the ends of the split ring. Between said ends and the key, rollers are provided that are capable of rolling with respect to said ends in response to withdrawal of the key and of resetting each time the key is withdrawn.

8 Claims, 5 Drawing Figures BACKGROUND -This invention relates to -'a'- ring latch for'releasably restraining a piston in a preselected position within a surrounding c'ylinder and, moreparticularly', felates to a latch of this type which employs'about the piston periphery a sp'l'it ring that is maintained in an expanded latchingcondition by a key which fits between the ends of'thesplit ringi' y w This general-type of latch is-shown in U. S. Pat. Nos. 3:6O4,87l-K'reichbaum and 3,646,2'92-Bark an et al; Also of interest' is my copending application Ser. No. 397,242; -filed- Sept-. "l4,-1973,-- now US. Pat. No.

-In this typeoflatch, the "split ring is usually located within a groove'in the pistonperiphery and, when in its expanded conditiom'engag'es an annular shoulder on the innerw'all of the cylinder that'blocks piston move mentpast the shoulder. This shoulder is shaped so that when the split'ringis'urged thereagainst, there is developed a-"force tending to contract the split ring into a non interfering position with respect tothe shoulder. Such contraction'is' normally prevented by the abovementioned key fitting between the ends of "the split ring; but when the ke'y is withdrawn from this position, the split-ring is'free to contract'into its non-interfering position, thus releasing the piston for movement within thecylinder. I)

In such a ring latch, the-latching force on the piston iswell distributed about theperiph'ery of the piston,

which-can be a very large area compared to the active area most latches. Partially as-a result of this,'a'relativ'elysmall releasing'force for withdrawing the abovedescribed key can be used to release a very large force on the piston. In a typical ring latch, the force being released may be in the neighborhood of 100times the releasing force, as compared to about S'tirnes with a simple prop latch. (The ratio ofthe force being released to the releasing force is'referred to herein as the mechani cal advantage of the latch).

. SUMMARY- An object of *the present invention is to' provide means'for substantially increasing the mechanical advantage of a ring-type'latch as compared to that present with'p'rior ring-type latches. l

The mechanical'advanta'ge of a ring-type latch depends to a significant extent uponthe opposition to withdrawal of the key-typelatching member that results from the ends of the split 'ring being pressed thereagainst by forces tending to contract the split ring. Another object of my invention is to provide, between the ends 'of the s'plit ring and the key, rollerswhich are capabl e of materially reducingthe force required to 'withdraw the key against this opposition." j

Still another object is 1) to mountthese rollers in such a mannerthatthey 'canbodily move by rolling with respect'to the split ringwhile the key is being withdrawn and (2) to return ther'oller's' topredetermined normal positions'leach time the key'is withdrawn imine diately following such withdrawal.

In carrying out the invention in'one form, [provide on each end of the split ring a roller that is positioned between" said end and the key-type latching member. Each of said ends has a surface on which the associated roller rolls in response to withdrawal of the latching member from its position betweenthe ends of the split ring. Each roller is retained in position on its associated surface by spring means that: (1) allows the roller to bodily moveaway from a predetermined initial position as itrolls' in-response to withdrawal of the latching member and (2) immediately returns the rollerto said predetermined initial position when the latching memher is sufficiently withdrawn to-separate from the rolle'rs l y BRIEF DESCRIPTION OF DRAWINGS,

For a better understanding of the invention, reference-may be had to-the following-description taken in conjunction with the accompanying drawings, wherein: FIG. 1 is a cross-section"view through a piston and cylinder as'sembly'comprising a prior-art ring latch. FIG. 2- is'a' sectional view along the*line-22 of FIG.

- FIG. 3'isan enlarged sectional view of a portion of a-ring latch embodying one form of my invention.

FIG. 4 is 'a sectional view along the line 4-4 of FIG.

FIG. '5 is a reduced scale view-partly in section showing a piston-and cylinder assembly including thering latch of FIGS. Sand 4. I

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referrin g now'to FIGS. 1 and 2, there is shown a prior art ring latch 10 similar to that shown in U.S.'Pat. No. 3,646,292-Barkan et aL'This ring latch cooperates with a cylinder 12 and a piston 14 to releasably restrain the-piston from moving within the cylinderout of its position depictedin FIGS; 1' and 2. It will be assumed, for discussion purposes, that "the cylinder 12 -is a stationary element, and the piston -14 is reciprocable within'the cylinder. It-will be further assumed that the piston as shown in FIG, 2 is biased in a downward direction by a high force F but is normally restrained by the-latch from moving downwardly. r a

The ring latch 10 comprises a split ring 20 of circular cross-section'that is carried in an annular groove 22 in the piston 14. This piston ring 20 is a resilient member that has a tendency to expand slightly in diameter, but its expansion is limited by-the internalwall of the cylinder I2 and, specifically, by a conical shoulder 23 on the internal wall of the cylinder 12.

The downward force Fon piston 14 is transmitted to piston ring 20 through groove surface 24 and urges the piston ring against conical shoulder 23. The reaction forcedeveloped on the ring by the conical shoulder tends to contract the ring. The ring is normally pre-' vented from contracting beyond the position shown in FIGS: '1 and 2 by a key'28, shown in'FIG. 1, that fits between the ends of the split ring. This key is occasionally referred to hereinafter as a latching member. When the key 28 is withdrawn radially outward from its position of FIG. 1, the reaction force from the conical'shoulder 23 on the cylinder forces the ringrapidly to contract completely into the groove 22, thus releasing the piston for downward movement. As'soonas this occurs, the biasing force F acting downwardly on the piston moves it"rapi dly downward within the cylinder."

In a ring latch shown at 10, the latching forceon the piston is well distributed around the periphery of the piston,'which is a very large area compared to the latching area in most latches; and, partially as a result of this, a relatively small force, applied in a radially outward direction to the key 28, can be used to release a very large force F on the piston. As previously pointed out,-the ratio of the force F being released to the releasing force F,', (i.e., the force applied to the key in order to, withdraw it) is referred to as the mechanical advantage 'of the latch.

For applying a radially-outward force F to the key 28 to effect tripping of the ring latch 10, a solenoid 30 is provided. This solenoid, which is preferably of the repulsion type, has its stationary coil structure 32 mounted on the stationary cylinderand its movable armature 34 coupled to the latching element 28. When the coil structure is appropriately energized, the armature 34 is repelled therefrom, and it moves at high speed to rapidly withdraw the key 28 from between the ends of piston ring 20 to release the ring latch. A suitable resetting spring 36 provides a force which tends to reset the armature to its normal position of FIG. 1 after such areleasing operation.

As pointed out hereinabove, an object of my invention is to increase the mechanical advantage of a ringtype latch such as.depicted in FIGS. 1 and 2, thereby reducing the force needed for withdrawing the latching member, or key, 28. For effecting such increase in mechanical advantage, I construct the ring latch as shown in FIGS. 3 and 4'.

In this ring latch, the ring 20 is provided at each end with an end member in the form of a block 40 of a substantially larger transverse cross-section than the ring itself, as viewed in planes extending radially of the ring. Each of these blocks 40 is joined an end of to the ring 20 by a suitable brazed joint 4.1. Each block 40 has a substantially planar surface 43 facing the key 28; and on this-planar surface, there is mounted a roller 45, preferably of hardened steel, that is adapted to engage the key 28 when thelatch is in its latching position.

For retaining and positioning the roller 45 on its block 40, a leaf spring 47 is provided for each block. As shown in FIGS. 2'and 3 this leaf spring 47 has a U- shaped back portion, one leg of which is clamped between a retaining element 49 and block 40, and a front portion extending transversely of the legs of the U- shaped portion. As shown in FIG. 4, the front portion comprises two spaced-apart arms 50. Each arm is loopeda'round one end of roller 45, as shown in FIG. 3, to form a journal that rotatably receives the roller end. The ends of the roller 45 that receive the loops 69 are of reduced diameter, thus assuring that the arms 50 and loops 69 will not project out past the periphery of the roller proper in'the region where the roller engages the key 28. v

For preventing roller 45 from moving substantially with respect to its block 40 in a direction along the roller axis, the block is provided with spaced-apart rails 53 that extend along the upper and lower edges of the block, as viewed in FIG. 4. For preventing the roller 45 from falling off the back of the block 40, a stop 54 is provided on the inner face of the block. The leaf spring 47 exerts a biasing force on the roller tending to hold it against this stop 54. This biasing force is also in a direction-to hold the roller 45 against the planar surface 43. The spring 47 also serves to prevent the roller 45 from dropping off the front of the block 40. In this respect, one leg 55 of the U-shaped portion of the spring 47 engages the back of the block before the roller can reach the front of the block when displaced from stop When the latch 10 is in its latching position of FIG. 3, the previously-described force tending to contract the split ring 20 urges the blocks 40 toward. the key 28 and thus presses the rollers 45 against the key with high forces. With no rollers present, as in FIGS. z] and 2, these forces can develop relatively high. frictional forces opposing withdrawal of the key 28. But the presence of the rollers results in a large reduction in these frictional opposing forces. More specifically, when the key 28 is withdrawn in a radially-outward direction from its position of FIG. 3 between-the ends-of thesplit ring, a rolling action is produced between the key,28 and the roller and between the'roller and the: surface 43 of its block. While the key and roller remain in contact as the key is withdrawn, the roller bodily moves by rolling action, causing its axis of rotation to shift, or translate, in the direction of rolling along the surface 43 a distance approximately half that moved by the'key 28.

When the key 28 has finally moved a sufficient distance so that the rollers 45 can no longer engage'its sur-- faces, the ring 20 isfree to contract at high speed under the influence of the above-described contracting force on the ring 20. This produces the previously-described tripping of the latch, thus releasing the piston 12 for movement with respect. to cylinder 14. In response to such release, the piston, biased for force F, moves rapidly downward into its dotted-line position of FIG. 5. When the key 28 is completely withdrawn from between the two end structures 40,45 of the vring 20, these end structures move toward each other, but only sufficiently to allow the ring 20 to contact into a noninterfering position with respect, to shoulder 23 on the cylinder. The ring 20.does not contract sufficientlyto allow the two end structures to engage.

When the key 28 is being withdrawn from its position of FIG. 3 during tripping of the. latch, each roller 45, ,in rolling along surface 43, is displaced from its stop 54.

The spring 47 associated with the roller exerts a biasing. force on it tending to return it to its normal position against the stop 54 but is ineffective to produce such return until the key 28 has moved out of engagement with the roller. When this does occur, the spring 47 rapidly resets its roller to its normal position of FIG. 3

against stop 54. The importance of this roller-resettin action will soon appear more clearly. When the piston 14 is displaced from its latched posi-, tion after key 28 has been withdrawn, the key is maintained in its withdrawn position by a hardened tongue portion on the piston, along which the inner surface of the key slides. This tongue portion is shown in FIG. 5. at 57.

Resetting of the piston 14 and the latch 10 is effected by returning the piston 14 in an upward direction from its unlatched dotted-line position of FIG. 5 to its origi: nal solid-line position. A suitable spring 60 beneath the piston effects such resetting in response to a predetermined drop in the downward force F on the piston.

When the upwardly-moving piston enters and passes slightly above its solid-line position of FIG. 5 during such resetting, the split ring 20 is free to follow vits natural tendency to expand since the cylinder wall is no longer maintaining the ring contracted. Also, at this time the key 28 is free to move radially inward under the bias of its reset spring 36 to aid in producing such expansion of the split, ring 20. In moving radially inward, the tapered edges 62 of the key first engage the tapered surfaces 64 of the blocks and then engage the rollers 45 to promote such expansion of the split ring 20. At the end of each key-resetting operation, a stop 63 (FIG. 3) on the radially-inner wall of piston groove 22 terminates radially-inward resetting movement of key 28 in a precise predetermined position.

Suitable stops 65 on the cylinder wall limit upward resetting movement of the piston 14 beyond a predetermined position. After these stops have been encountered, the downward force F builds up and moves the piston downward slightly into its solid-line position of FIG. 5.

It is of considerable importance that the rollers 45 be positioned in the same location each time the latch is set. Then with a predetermined stroke of the key in a radially-outward direction, the latch trips when the rollers have moved the same distance on each operation. I assure such initial positioning of the rollers by utilizing the springs 47 to reset the rollers 45 to their original position against stop 54 for each latch-releasing operation. Since the rollers never engage each other or the opposite block 40, there is no interference from these parts with respect to roller-resetting. The key 28 is able to easily return to its set position of FIG. 3 without moving thev rollers out of their reset position of FIG. 3 because when the key moves radially inward along the rollers at the end of the above-described upward resetting travel of piston 14, split ring is free to expand slightly to allow the key 28 to reenter its set position with little opposition from the rollers. Although the rollers slide, rather than roll, on the surface 43 in response to resetting movement of the key 28, this sliding is not a significant problem since there is then no large force pressing the rollers against the key in view of the expansion capabilities of the ring during this brief period.

Another feature contributing to consistent tripping of the latch after a predetermined travel of the key 28 in a radially-outward direction is the stop 63. By consistently terminating resetting of the key 28 in the same position (that of FIG. 3), I assure that the tripping stroke of the key is consistently initiated from the same position. Since motion of the rollers is also consistently initiated from the same position, as above described, the key consistently separates from the rollers after substantially the same radially-outward travel of the key on each tripping operation.

It is of further significance that the rollers are positioned to provide balanced forces by the key during key resetting. In this respect, note that during key-resetting, the axes of both rollers are positioned in a single plane 66 perpendicular to the longitudinal axis of the key.

For ideal rolling action of the rollers during a releasing operation, each roller should have its axis perpendicular to the direction of motion of the key 28. The springs 47 maintain substantially this perpendicular relationship during the period the key is being withdrawn.

It is highly desirable that neither of the arms 50 of each spring 47 rub against the key 28. To reduce the chances for such rubbing, especially when the piston is moving through its initial downward travel during tripping or through its final upward travel during resetting, each roller is provided with the previously-described reduced-diameter end portions for receiving the spring loops 69, and the spring loops are of a smaller diameter than the roller proper. This, in effect, shields the loops 69 from rubbing contact with the key 28. The abovedescribed relationship between the diameter of the roller and that of the loops can also be expressed in the following terms. The periphery of the roller portion located between the spring loops 69 is radially spaced from the roller axis by a greater amount than the outer surface of the loops in the region facing the key 28.

As mentioned hereinabove, each of the springs 47 applies a force to its roller that pushes the roller against surface 43. This desirably reduces chatter of the roller during roller resetting when it is returning to its position against stop 54. This latter force does develop some friction between the roller and the spring within the journal formed by loop 69. But by reducing the diameter of the roller in this region, I reduce the diameter of the friction circle and thus advantageously reduce the friction torque on the roller.

To prevent the split ring 20 from shifting circumferentially with respect to the piston 14, a suitable pin and slot connection is provided at a location on the split ring approximately 180 degrees from the location of key 28. Since this connection is not a part of the present invention, it has not been illustrated.

It is noted that when the split ring 20 is in its contracted condition, the end blocks 40 do not project radially outward from the piston 14 beyond its outer periphery. (This will be evident from FIG. 3 where it can be ssen that blocks 40 are located wholly within a reference circle 73 coinciding with the outer perhphery of ring 20.) This non-projecting relationship is advantageous because it obviates any need to provide a recess in the internal wall of the cylinder 12 to accommodate the blocks 40 when the piston travels within the cylinder. The absence of such recess is desirable not only because it eliminates any need for forming the recess but also because itmakes it easier to provide a seal, as may sometimes be needed, between the piston and the cylinder. Such a seal can take the form of a simple 0- ring 70 (FIG. 5) provided in the piston in a location just below, but immediately adjacent, the ring latch. Note that this O-ring is not required to pass over any such recess when the piston moves downward from its solid line position of FIG. 5, and this helps lengthen the seals life and improve its sealing ability.

While I have shown and described in particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention in its broader aspects; and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a cylinder, a piston reciprocable within said cylinder, means biasing said piston in a predetermined direction within said cylinder, and latching means for releasably restraining said piston with respect to said cylinder against said biasing means, said latching means comprising:

a. a circumferentially extending groove in the periphery of said piston,

b. a split ring located in said groove and extending about the periphery of said piston, said ring having a pair of ends that are spaced apart when said ring is in its expanded condition,

c. end members located between theends of said ring and being of substantially larger cross section than the ring as viewed in sectional planes extending radially of the ring,

d. a radially-movable latching member located between said end members and normally holding said ring in its expanded condition, and means for radi ally moving said latching member,

e. a generally annular shoulder onsaid cylinder for engaging said split ring whenthe ring is expanded in a manner'tending to force said split'ring to contract within said grooveinto a non-interfering position with. respectto' said shoulder when the split ring is urged bysaidpiston-biasing means against said shoulder, 1 Y t f. said'contraction normally being prevented by said latching member but occurring in response to withdrawal of said latching member from its position between the said'end members,

.g. a first roller located between said latching member j. and retaining means for retaining saidrollersin po-. sition on said end member surfaces before, during,

and after said rolling action and allowing the axis of rotation of eachroller to shift during said rolling action.

2. The combination of claim l-in which:

a. each of said end members comprises a stop for limiting movement of the roller thereon in a direction radiallyof said ring,

b. said retaining means comprises spring means for biasing the associated roller into a normal position against-said stop,

' c. each of said rollers moves away from its associated stop when rolling in response to said withdrawal of said latching member, and

cl. said spring means returns-said rollers to said normal positions against their respective stops after withdrawal of said latching member sufficiently to separate the latching member from said rollers-and before return of said latching member to its position between said rollers.

3. The combination of claim 1 in which said retaining means comprises spring means biasing said rollers toward normal positions whichthe rollers occupy when said latching'member is in its fully-inserted position between said end members, said spring means maintaining said rollers during rolling in positions wherein the axes of the rollers extend substantially perpendicular to the path of movement of said latching member.

4. The combination of claim 3 in which each of said end members comprises a pair of spaced-apart rails extending parallel to the path of movement of the roller associated with said end member, said rails being located immediately adjacent the opposed: ends of the associated roller so as to limit shifting of said associated roller along its axis.

5. The combination of claim 1 inwhich each of said end members comprises a block including said surface on which an associated" roller rolls, said blocks being located radially inwardly of the outer periphery of said piston when said latching member is withdrawn, thus obviating any need for a recess in the internal Wall of said cylinder to accommodate said blocks during piston movement. I

6. The combination of claim 1 in which: (a) said retaining-means comprises spring means biasing said rollers toward the respective surfaces of said end members on which the rollers roll, (b) said rollers have reduceddiameter ends that are journaled in their associated retaining means, and (c) the portion of each roller between said end members is positioned to bear against said latching member when the latching member is in its normal position holding said ring expanded.

7. In combination, a cylinder, a piston reciprocable within said cylinder, me'ans' biasing said piston in a predetermined direction within said cylinder, and latching means for releasably restraining said piston with respect 'tosaid cylinder against said biasing means, said latching means comprising: i

a. a circur'nferentially extending groove in the periphcry of said piston,

' b. a split ring located in said groove and extending about the periphery of said piston, said ring having a pair of ends that are spaced apart when said ring is in itsexpanded condition,

c. end members located between the ends ofsaid ring and being of substantially larger cross section than the ring as viewed in sectional planes extending radially of the ring,

d. a radially-movable latching member located between said end members and normally holding said ring in its expanded condition, and means for radially moving said latching member,

e. a generally annular shoulder on said cylinder for engaging said split ring when the ring is expanded in a manner tending to force said split ring to contract within said groove into a non-interfering position with respect to said shoulder when the split ring is urged by said piston-biasingmeans against said shoulder, p v

f. said contraction normally being prevented by said latching member but occurring in response to withdrawal of said latching member from its position between the said end members,

g. a first roller located between said latching member and one of said end members and a second roller located between said latching member and the other of said end members, 7

h. said end members having surfaces on which said first and second rollers respectively roll in response to withdrawal of said latching member,

i. and retaining means for retaining said rollers in position on said end member surfaces before, during, and after said rolling action and allowing the axis of rotation of each roller to shift during said rolling action,

j. said retaining means comprising spring means bias- 7 ing said rollers toward normal positions which the rollers occupy when said latching memberis in its fully-inserted position between said end members said spring means maintaining said rollers during I rolling in positions wherein the axes of the rollers extend substantially perpendicular to the path of movement of said latching member, I

8. The combination of claim 7 in which the portion of the roller located between said spaced arms is radially spaced from the roller axis by a greater amount that the outer surface of said spaced arms in the region facing said latching member, thereby shielding said arms from rubbing engagement with said latching member. 

1. In combination, a cylinder, a piston reciprocable within said cylinder, means biasing said piston in a predetermined direction within said cylinder, and latching means for releasably restraining said piston with respect to said cylinder against said biasing means, said latching means comprising: a. a circumferentially extending groove in the periphery of said piston, b. a split ring located in said groove and extending about the periphery of said piston, said ring having a pair of ends that are spaced apart when said ring is in its expanded condition, c. end members located between the ends of said ring and being of substantially larger cross section than the ring as viewed in sectional planes extending radially of the ring, d. a radially-movable latching member located between said end members and normally holding said ring in its expanded condition, and means for radially moving said latching member, e. a generally annular shoulder on said cylinder for engaging said split ring when the ring is expanded in a manner tending to force said split ring to contract within said groove into a non-interfering position with respect to said shoulder when the split ring is urged by said piston-biasing means against said shoulder, f. said contraction normally being prevented by said latching member but occurring in response to withdrawal of said latching member from its position between the said end members, g. a first roller located between said latching member and one of said end members and a second roller located between said latching member and the other of said end members, h. said end members having surfaces on which said first and second rollers respectively roll in response to withdrawal of said latching member, i. each roller also rolling on said latching member during withdrawal of said latching member so tht said rolling action causes a shift of the axis of rotation of said roller relative to its associated end member in the direction of rolling, j. and retaining means for retaining said rollers in position on said end member surfaces before, during, and after said rolling action and allowing the axis of rotation of each roller to shift during said rolling action.
 2. The combination of claim 1 in which: a. each of said end members comprises a stop for limiting movement of the roller thereon in a direction radially of said ring, b. said retaining Means comprises spring means for biasing the associated roller into a normal position against said stop, c. each of said rollers moves away from its associated stop when rolling in response to said withdrawal of said latching member, and d. said spring means returns said rollers to said normal positions against their respective stops after withdrawal of said latching member sufficiently to separate the latching member from said rollers and before return of said latching member to its position between said rollers.
 3. The combination of claim 1 in which said retaining means comprises spring means biasing said rollers toward normal positions which the rollers occupy when said latching member is in its fully-inserted position between said end members, said spring means maintaining said rollers during rolling in positions wherein the axes of the rollers extend substantially perpendicular to the path of movement of said latching member.
 4. The combination of claim 3 in which each of said end members comprises a pair of spaced-apart rails extending parallel to the path of movement of the roller associated with said end member, said rails being located immediately adjacent the opposed ends of the associated roller so as to limit shifting of said associated roller along its axis.
 5. The combination of claim 1 in which each of said end members comprises a block including said surface on which an associated roller rolls, said blocks being located radially inwardly of the outer periphery of said piston when said latching member is withdrawn, thus obviating any need for a recess in the internal wall of said cylinder to accommodate said blocks during piston movement.
 6. The combination of claim 1 in which: (a) said retaining means comprises spring means biasing said rollers toward the respective surfaces of said end members on which the rollers roll, (b) said rollers have reduced-diameter ends that are journaled in their associated retaining means, and (c) the portion of each roller between said end members is positioned to bear against said latching member when the latching member is in its normal position holding said ring expanded.
 7. In combination, a cylinder, a piston reciprocable within said cylinder, means biasing said piston in a predetermined direction within said cylinder, and latching means for releasably restraining said piston with respect to said cylinder against said biasing means, said latching means comprising: a. a circumferentially extending groove in the periphery of said piston, b. a split ring located in said groove and extending about the periphery of said piston, said ring having a pair of ends that are spaced apart when said ring is in its expanded condition, c. end members located between the ends of said ring and being of substantially larger cross section than the ring as viewed in sectional planes extending radially of the ring, d. a radially-movable latching member located between said end members and normally holding said ring in its expanded condition, and means for radially moving said latching member, e. a generally annular shoulder on said cylinder for engaging said split ring when the ring is expanded in a manner tending to force said split ring to contract within said groove into a non-interfering position with respect to said shoulder when the split ring is urged by said piston-biasing means against said shoulder, f. said contraction normally being prevented by said latching member but occurring in response to withdrawal of said latching member from its position between the said end members, g. a first roller located between said latching member and one of said end members and a second roller located between said latching member and the other of said end members, h. said end members having surfaces on which said first and second rollers respectively roll in response to withdrawal of said latching member, i. and retaining means for retaining said rollers in position on said End member surfaces before, during, and after said rolling action and allowing the axis of rotation of each roller to shift during said rolling action, j. said retaining means comprising spring means biasing said rollers toward normal positions which the rollers occupy when said latching member is in its fully-inserted position between said end members, said spring means maintaining said rollers during rolling in positions wherein the axes of the rollers extend substantially perpendicular to the path of movement of said latching member, k. said spring means comprising leaf spring structure associated with each of said rollers, at least one of said leaf spring structures comprising a pair of spaced arms for receiving the ends of its associated roller in journaled relationship, the portion of said roller located between said spaced arms being positioned to bear against said latching member when the latching member is in its normal position holding said ring expanded.
 8. The combination of claim 7 in which the portion of the roller located between said spaced arms is radially spaced from the roller axis by a greater amount that the outer surface of said spaced arms in the region facing said latching member, thereby shielding said arms from rubbing engagement with said latching member. 